This invention relates to the field of electronic signal processing, and more specifically to a received signal strength indicator (RSSI) with an arbitrarily shaped transfer function.
An RSSI circuit measures the instantaneous power of a time-varying electrical signal, usually a voltage.
RSSI circuits usually comprise a voltage squarer, followed by a low-pass filter which removes the spectral content located at twice the modulating frequency and above. The output of the RSSI is usually a voltage, proportional to the instantaneous power of the input signal. Hence, these circuits provide a linear relationship between the output and the power of the input signal. In many applications, it is however desirable to obtain a non-linear such relationship. In the art logarithmic amplifiers are known, which shape the input power by a logarithmic transfer function, which is a particular case of a non-linear function. It is desirable to create a circuit which shapes the power of the input signal according to an arbitrary monotonic function. A conventional solution uses an A/D converter which digitizes the linear RSSI, and then applies to it an arbitrary transfer function in the digital domain. This solution has the drawback of complexity and high power consumption, since both the analog RSSI circuit and the A/D must have a full-scale high enough to handle signals covering the entire required dynamic range, and a resolution such that it is able to discriminate the smallest difference required by the transfer function.
It would be desirable, therefore, to create an arbitrarily shaped RSSI circuit which does not require a high-resolution ADC and uses low power.